Being an old C programmer I'd like to suggest a library, Text.Printf,
for C printf() style formatting.
For example
do
printf "Hello, world\n"
printf "%s, cruel %s\n" "Goodbye" "world"
printf "pi is about %10.8f\n" (pi::Double)
I have a Haskell 98 implementation of this function if people feel
that it would be useful.
-- Lennart